Three is a crowd - inefficient communication in the multi-player electronic mail game

In a two-player stag hunt with asymmetric information, players may lock each other into requiring a large number of confirmations and confirmations of confirmations from one another before eventually acting. This intuition has been formalized in the electronic mail game (EMG). The literature provides extensions on the EMG that eliminate inefficient equilibria, suggesting that no formal rules are needed to prevent players from playing inefficiently. The present paper investigates whether these results extend to the multi-player EMG. We show that standard equilibrium refinements cannot eliminate inefficient equilibria. While two players are predicted to play efficiently, many players need formal rules telling them when who talks to whom.Multi-Player Electronic Mail Game, Collective Action, Communication Networks

Risk Minimizing Evacuation Strategies under Uncertainty

This paper presents results on the simulation of the evacuation of the city of Padang with approximately 1,000,000 inhabitants. The model used is MATSim (www.matsim.org). Three different strategies were applied: shortest path solution, user optimum, system optimum, together with a constraint that moves should reduce risk whenever possible. The introduction of the risk minimization increases the overall required safe egress time (RSET). The differences between the RSET for the three risk minimizing strategies are small. Further quantities used for the assessment of the evacuation are the formation of congestion and the individual RSETs (in comparison with the available SET).BMBF, 03G0666E, Verbundprojekt FW: Last-mile Evacuation; Vorhaben: Evakuierungsanalyse und Verkehrsoptimierung, Evakuierungsplan einer Stadt - Sonderprogramm GEOTECHNOLOGIENBMBF, 03NAPAI4, Transport und Verkehr: Verbundprojekt ADVEST: Adaptive Verkehrssteuerung; Teilprojekt Verkehrsplanung und Verkehrssteuerung in Megacitie

Simplicity of beliefs and delay tactics in a concession game

I explore the idea of simplicity as a belief-selection criterion in games. A pair of strategies in finite-automata representation (s(1), s(2)) is a Simple Nash Equilibrium (SINE) if: (1) s(j) is a best-reply to s(i); (2) every automaton for player j, which generates the same path as s(j) (given s(i)), has at least as many states as s(j). I apply SINE to a bilateral concession game and show that it captures an aspect of bargaining behavior: players employ delay tactics in order to justify their concessions. Delay tactics are mutually reinforcing, and this may prevent players from reaching an interior agreement. (C) 2003 Elsevier Inc. All rights reserved

Bounding Rationality by Discounting Time

Consider a game where Alice generates an integer and Bob wins if he can factor that integer. Traditional game theory tells us that Bob will always win this game even though in practice Alice will win given our usual assumptions about the hardness of factoring. We define a new notion of bounded rationality, where the payoffs of players are discounted by the computation time they take to produce their actions. We use this notion to give a direct correspondence between the existence of equilibria where Alice has a winning strategy and the hardness of factoring. Namely, under a natural assumption on the discount rates, there is an equilibriumwhere Alice has a winning strategy iff there is a linear-time samplable distribution with respect to which Factoring is hard on average. We also give general results for discounted games over countable action spaces, including showing that any game with bounded and computable payoffs has an equilibrium in our model, even if each player is allowed a countable number of actions. It follows, for example, that the Largest Integer game has an equilibrium in our model though it has no Nash equilibria or epsilon-Nash equilibria.Comment: To appear in Proceedings of The First Symposium on Innovations in Computer Scienc

The Structure of Information Networks

We develop a model of information acquisition in a network where agents pay for all the information they acquire including those through indirect links. The cost of information depends on the value of information itself and the distance it traverses in the network. We find that when the costs of information increase with distance, the complete network is the only Nash network. When costs of information decrease with distance capturing delay, all equilibrium information networks are minimally connected, though not all trees are Nash. We analyze the popular star and chain networks and identify strict Nash networks. We show that there is almost no divergence between efficient and equilibrium information networks. We explore the implications of a spatial model and information decay and discuss the relationship with experimental evidence.Nash networks, information networks, efficient networks

Genome-driven evolutionary game theory helps understand the rise of metabolic interdependencies in microbial communities

Metabolite exchanges in microbial communities give rise to ecological interactions that govern ecosystem diversity and stability. It is unclear, however, how the rise of these interactions varies across metabolites and organisms. Here we address this question by integrating genome-scale models of metabolism with evolutionary game theory. Specifically, we use microbial fitness values estimated by metabolic models to infer evolutionarily stable interactions in multi-species microbial “games”. We first validate our approach using a well-characterized yeast cheater-cooperator system. We next perform over 80,000 in silico experiments to infer how metabolic interdependencies mediated by amino acid leakage in Escherichia coli vary across 189 amino acid pairs. While most pairs display shared patterns of inter-species interactions, multiple deviations are caused by pleiotropy and epistasis in metabolism. Furthermore, simulated invasion experiments reveal possible paths to obligate cross-feeding. Our study provides genomically driven insight into the rise of ecological interactions, with implications for microbiome research and synthetic ecology.We gratefully acknowledge funding from the Defense Advanced Research Projects Agency (Purchase Request No. HR0011515303, Contract No. HR0011-15-C-0091), the U.S. Department of Energy (Grants DE-SC0004962 and DE-SC0012627), the NIH (Grants 5R01DE024468 and R01GM121950), the national Science Foundation (Grants 1457695 and NSFOCE-BSF 1635070), MURI Grant W911NF-12-1-0390, the Human Frontiers Science Program (grant RGP0020/2016), and the Boston University Interdisciplinary Biomedical Research Office ARC grant on Systems Biology Approaches to Microbiome Research. We also thank Dr Kirill Korolev and members of the Segre Lab for their invaluable feedback on this work. (HR0011515303 - Defense Advanced Research Projects Agency; HR0011-15-C-0091 - Defense Advanced Research Projects Agency; DE-SC0004962 - U.S. Department of Energy; DE-SC0012627 - U.S. Department of Energy; 5R01DE024468 - NIH; R01GM121950 - NIH; 1457695 - national Science Foundation; NSFOCE-BSF 1635070 - national Science Foundation; W911NF-12-1-0390 - MURI; RGP0020/2016 - Human Frontiers Science Program; Boston University Interdisciplinary Biomedical Research Office ARC)Published versio

Multiple Equilibria in the Welfare State

Excess distortions in the welfare state might be the consequence of the government's lack of ability to commit not to help "unlucky" agents. Incentive considerations that are crucial in standard insurance in the presence of moral hazard, plays no role in this case. As a consequence, the government might provide too much insurance. Still, equilibria with incomplete insurance and above-minimum effort might arise. Two possible reasons for multiple equilibria are explored in the paper, namely that marginal utility of consumption is positively associated with effort and that economic policy is costly. It is shown that the equilibria can be Pareto rankable. Borrowing analytical tools from recent developments in dynamic games (Matsui and Matsuyama, 1995), stability conditions of different equilibria are analyzed.

Heterogeneity and Link Imperfections in Nash Networks

Heterogeneity in Nash networks with two-way flow can arise due to differences in the follow- ing four variables: (i) the value of information held by players, (ii) the rate at which information decays as it traverses the network, (iii) the probability with which a link transmits information, and (iv) the cost of forming a link. Observe that the second and third forms of heterogeneity are also instances of link imperfections. In sharp contrast to the homogeneous cases in this paper we show that for any type of link imperfection, under heterogeneity involving only two degrees of freedom, all networks can be supported as Nash or efficient. To address the question of conflict between stability and efficiency, we then identify conditions under which efficient networks are also Nash. We also find that cost heterogeneity leads to non-existence of Nash networks in models with and without link imperfections. We show that in general there is no relationship between the decay and probabilistic models of network formation. Finally, we show that on reducing heterogeneity the earlier “anything goes” result disappears.